Bug FAQKnopper Gall Wasp
Andricus quercuscalicis · Order: Hymenoptera · Family: Cynipidae
Also called: Knopper Gall
Knopper galls are about 2 cm long, green to yellow-green, ridged and initially sticky, forming on oak buds and later breaking out between the cup and the acorn. The wasp has a two-phase life cycle that needs both Turkey oak and pedunculate (or sometimes sessile) oak, with spring galls on Turkey oak catkins and autumn galls on pedunculate oak acorns.
Source: Wikipedia
How to recognize it
The gall appears as a green to yellow-green, ridged, sticky mass on the oak bud that later breaks out between the cup and the acorn.
Source: Wikipedia
Size
The gall grows to about 2 cm in size.
Source: Wikipedia
How to get rid of it
Control measures are considered unnecessary because the wasp has not caused serious damage to acorn fertility.
Source: Wikipedia
Where it lives
Knopper galls form on pedunculate oak where the wasp lays eggs in buds, and they are most common on old country and urban estates that have Turkey oak planted.
Source: Wikipedia
What it eats
The species needs both pedunculate (or occasionally sessile) oak and Turkey oak to complete its life cycle.
Source: Wikipedia
Life cycle
It has an obligate two-phase life cycle: a spring generation that forms small conical galls on Turkey oak catkins and reproduces parthenogenetically, and an autumn generation that creates the knopper galls on pedunculate oak acorns after mating.
Source: Wikipedia
When you see it
The galls turn woody and brown in early autumn, fall from the tree, and the adult females emerge from a vent in the gall in spring.
Source: Wikipedia
Where it comes from
The wasp originally occurred where Turkey oak grows in south-eastern Europe and has recently spread to Great Britain and Ireland.
Source: Wikipedia
Lookalikes
Knopper galls can be confused with acorn cup galls caused by Andricus grossulariae, but they are usually distinctive.
Source: Wikipedia
More photos
Questions people ask
How can I tell a knopper gall from an acorn cup gall?
Knopper galls are usually distinctive, but they may look like acorn cup galls caused by Andricus grossulariae under certain growth conditions.
Source: Wikipedia
Do knopper gall wasps need more than one type of oak?
Yes, they require both Turkey oak and pedunculate (or sometimes sessile) oak to complete their two-phase life cycle.
Source: Wikipedia
Same family (Cynipidae)
Sources
- Wikipedia: https://en.wikipedia.org/wiki/Andricus_quercuscalicis
Look it up elsewhere: GBIF · iNaturalist · BugGuide · Wikipedia
Text written 2026-10-24 from the sources above and checked sentence by sentence against them. Data fetched 2026-10-22.